Pathogen and particle detector system and method

ABSTRACT

A particle detector has a sample area of cross section no in excess of about 2 mm for containing environmental fluid, a light source on one side of the sample area for directing a collimated or nearly collimated beam of light through the sample air or water so that part of the light beam will be scattered by any particles present in the air or water while the remainder remains unscattered, and a beam diverting device on the opposite side of the sample area for diverting or blocking at least the unscattered portion of the beam of light and directing at least part of the scattered light onto a detector. The detector produces output pulses in which each pulse has a height proportional to particle size and a pulse height discriminator obtains the size distribution of airborne particles detected in the air or water sample at a given time from the detector output. The detector may also include a device for discriminating between biological agents and inorganic particles.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to four copending U.S. provisionalapplications: Ser. No. 60/592,618, entitled, “Pathogen Detector Systemand Method,” filed Jul. 30, 2004; Ser. No. 60/592,619, entitled,“Particle Detector System and Method,” filed Jul. 30, 2004; Ser. No.60/606,212, entitled, “Pathogen Detector System and Method,” filed Sep.1, 2004; and Ser. No. 60/683,534, entitled, “Improvements in PathogenDetector Systems,” filed May, 20, 2005. All four copending U.S.provisional applications are entirely incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to a system and method fordetecting airborne or waterborne particles, and more particularly to asystem and method for detecting airborne or waterborne particles andclassifying the detected particles by size. The invention has particularutility in detecting and classifying by size allergens and biologicalwarfare agents in fluids, i.e., airborne or waterborne particles, andwill be described in connection with such utility, although otherutilities are contemplated.

BACKGROUND OF THE INVENTION

An urban terrorist attack involving release of biological warfare agentssuch as bacillus anthracis (anthrax) is presently a realistic concern.Weaponized anthrax spores are extremely dangerous because they can gainpassage into the human lungs. A lethal inhalation dose of anthrax sporesfor humans, LD₅₀ (lethal dose sufficient to kill 50% of the personsexposed) is estimated to be 2,500 to 50,000 spores (see T. V. Inglesby,et al., “Anthrax as a Biological Weapon”, JAMA, vol. 281, page 1735,1999). Some other potential weaponized bio-agents are yersinia pestis(plague), clostidium botulinum (botulism), and francisella tularensis.In view of this potential threat, there is currently a need for an earlywarning system to detect such an attack.

Laser particle counters are known in which a laser beam is directedthrough a sample and the light, which travels through the sample, isdetected and analyzed to detect scattered light from particles in thesample. One problem with existing detectors or particle counters which,are designed for detection of scattered light is that the scatteringsignal must be extracted from the incident illumination light sourcesignal. This involves detecting a weak signal (scattering from smallparticles) from a very noisy background (glare from the laser source).Currently, conventionally designed laser particle counters are fragileand expensive, and unsuited to this application. The conventionaltechniques used for laser particle counting include the laser Dopplermethod, which measures the speed of the particle and deduces sizeinformation, the transient time method which measures the time neededfor particles to traverse a sensing region, and large angle multi-sensordesign, which is capable of measuring only small particles. A proposedbio-sensor based on laser-induced fluorescence using a pulsed UV laseris described by T. H. Jeys, et al., Proc. IRIS Active Systems, Vol. 1,p. 235, 1998. This is capable of detecting an aerosol concentration offive particles per liter of air, but involves expensive and delicateinstruments. See also Hairston et al., J. Aerosol Sci., Vol. 28, No. 3,p. 471-482 (1997). Other particle counters are manufactured by Met OneInstrument, Inc, of Grants Pass, Oregon, Particle Measurement Systems,Inc., of Boulder, Colo., and Terra Universal Corp., of Anaheim, Calif.By virtue of their design, these particle counter configurations requireprecision optical alignment, as well as sophisticated sensors andelectronics. These products are geared towards laboratory use and costthousands of dollars for a single unit. Thus, they are not suitable fora field-deployed detector, nor are they designed specifically fordetection of biological warfare agents.

Various detectors have been designed to detect airborne allergenparticles and provide warning to sensitive individuals when the numberof particles within an air sample exceeds a predetermined minimum value.These are described in U.S. Pat. Nos. 5,646,597, 5,969,622, 5,986,555,6,008,729, and 6,087,947, all of Hamburger et al. These detectors allinvolve direction of a light beam through a sample of environmental airsuch that part of the beam will be scattered by any particles in theair, a beam blocking device for transmitting only light scattered in apredetermined angular range corresponding to the predetermined allergensize range, and a detector for detecting the transmitted light. An alarmis actuated if the light detected at the detector is above apredetermined level. Although these devices are sufficient for thepurpose of providing an alarm indication based on the presence ofallergen particles, they are not suitable for field deployment and donot meet the more stringent requirements for a pathogen detector fordetecting biological warfare agents.

SUMMARY OF THE INVENTION

The present invention provides a new and improved particle/pathogendetector system and method for detecting and classifying airborne orwaterborne particles.

According to one aspect of the present invention, a particle detectorsystem is provided, which comprises an outer housing having a samplearea for containing sample air or water, a light source for directing afocused beam of light through the sample air, or water whereby portionsof the beam of light are scattered at various angles by particles ofvarious sizes present in the sample area, and an unscattered portion ofthe beam of light remains unscattered, a beam blocking device forblocking at least the unscattered portion of the beam of light anddirecting at least part of the scattered light along a light path, adetector positioned in the light path after the beam blocking device fordetecting light directed by the beam blocking device onto the detector,and producing output pulses in which each pulse has a heightproportional to particle size, a pulse height discriminator forobtaining the size distribution of airborne or waterborne particles inthe sample at a given time, and an alarm unit for providing a warningsignal if the number of particles within a predetermined size range ofinterest. The beam blocking device will stop the unscattered incidentlaser beam, efficiently eliminating background noise caused by the lightsource, and then detecting the angular distribution and intensity oflight scattered by particles in an air or water sample, converting theoutput of the detector into a particle size distribution histogram, andproducing an alarm signal if the histogram indicates unusually largenumbers of particles within a predetermined size range. Thepredetermined size range will depend on the particles of interest. Forairborne mold, the size range of interest typically is about 1 to 3 μm;for airborne bio-agents the size range of interest typically is about 1to 7 μm; while for airborne allergens or other harmful substances suchas beryllium dust or asbestos the size range of interest typically isabout 5 to 50 μm. In the case of waterborne particles of interest, whichtypically may comprise bacteria or bacterial spores, the size range ofinterest typically is about 1 to 20 microns.

In an exemplary embodiment of the invention, the output of the pulseheight discriminator is connected to a processing unit for processingthe particle size distribution at a given time, based on the height ofeach pulse, producing a histogram of the airborne or waterborne particlesize distribution, and displaying the histogram on an output device. Thediscriminator may comprise a peak detector for measuring incoming pulseheight, and a comparator and register for registering the number ofpulses in each pulse height. The respective pulse heights are thenconverted into particle sizes, and a histogram of the particle sizedistribution is displayed on a suitable display unit, such as an LED orliquid crystal display, or a computer screen.

An alarm device may also be provided to produce an audible and/orvisible alarm signal if the number of pulses in a certain particle sizerange exceeds a predetermined normal background value. For example, inthe case where bio-agents are of interest any sudden and localizedincrease in the number of airborne particle counts in the size rangefrom 1 μm to 7 μm would normally signify an intentional release ofhostile bio-agents.

In an exemplary embodiment of the invention, a reflector is placed on orin front of the beam blocker in order to reflect part of the unscatteredportion of the incident light beam, and a second photodetector ispositioned to detect light reflected from the reflector. The function ofthe photodetector is to monitor the output of the light source, whichmay be a laser diode. This allows for self-calibration of the apparatus.The particle size measurement relies on the electrical pulse heightmeasurement, and it is therefore important to account for anyfluctuations in the laser diode power output. The electrical pulsesignal from the first detector may be divided by the monitoring signalfrom the second detector in order to ensure that the results are notaffected by any laser power variations. The output of the secondphotodetector is also monitored to indicate the laser diode performance.When the signal from the second photodetector falls below apredetermined level, such as 50% of the starting power level, a “LaserPower Low” alarm will sound, in order to initiate a maintenance call.

A transparent partition slide may be provided between the sample areaand the beam blocking device. The purpose of the slide is to preventdust or other environmental pollutants from reaching the opticalelements and photodetectors. This will be particularly beneficial whenthe system is used in harsh field deployment conditions. The slide isreplaced when it becomes too dirty to allow sufficient lighttransmission, which will be determined by the second photodetector.Thus, the laser power alarm may indicate either that the laser diode haslost power, or that the slide has become too dirty. A moderately dirtypartition slide will not affect the accuracy of particle detection,since it will reduce the light intensity of both the unscattered portionof the light beam and the scattered light beam, and the ratio of thesetwo signals is recorded.

According to another aspect of the present invention, a method ofdetecting and classifying by size airborne or waterborne particles isprovided, which comprises the steps of:

directing a light beam through a sample of air or water such that afirst portion of the light beam is scattered by particles present in thesample and a second portion remains unscattered;

receiving both portions of the light beam, which have passed through thesample, and directing the light beam portions onto a beam blockingdevice;

blocking at least the second portion of the light beam at the beamblocking device and direction at least part of the first portion of thelight beam onto a first detector;

measuring the pulse height of electrical pulses output from the firstdetector;

counting the number of pulses of each pulse height in a predeterminedtime interval;

converting the pulse heights to particle sizes;

counting number of pulses corresponding to each particle size; and

producing an alarm signal if the number of pulses detected within apredetermined size range is exceeded.

In an exemplary embodiment of the invention, the data regarding numberof pulses for each particle size is converted into a histogram of thedetected particle size distribution. This may then be compared to knownbio-agent particle size distributions, and an alarm may be activated ifthe detected distribution matches any known bio-agent particle sizedistribution. The size distribution may also be used to identify theparticular bio-agent detected, and may provide a forensic tool foridentifying the manufacturing process by which the weaponized bio-agentwas produced.

The particle detection system and method of this invention can be usedto detect the presence of airborne or waterborne biological warfareagents or other harmful substances including mold, bacterial, bacterialspores, and dusts such as beryllium and asbestos.

In another embodiment of the invention there is provided an improveddetection system and method which can be used to both detect thepresence of airborne or waterborne particles within a selected sizerange and also differentiate between biological organisms or biologicalagents and inert or inorganic substances within that selected sizerange. More particularly, the present invention provides an airborne orwaterborne particle detector in combination with a fluorescence sensorfor detecting and discriminating between airborne or waterborneparticles of living organisms or bio-agents from inert substances. Thesystem of the present invention detects particles of a given size rangeof interest, e.g., about 1 to about 7 microns, and differentiatesbetween biological organisms or biological agents and inert or inorganicsubstances within that size range.

In another aspect, the present invention provides an improved detectionsystem and method which can be used to both detect the presence ofairborne or waterborne particles within a selected size range and alsoto differentiate between biological organisms or biological agents andinert or inorganic substances within that selected size range.

Another embodiment of the present invention provides an improvedfluorescence detector and method by utilizing multiple detectionhousings. More specifically, a passageway in which a fluid containingbiological organisms or biological agents can flow is used to connect aseries of housings. Each housing contains a light source for sendinglight through the fluid and a detector positioned in the light path fordetecting the fluorescence and particle size of the biological organismsor biological agents and producing a corresponding output signal.Preferably, the light source is tuned to produce light of an optimalexcitation wavelength of one or more metabolites. For example, the lightsource may be tuned to the excitation wavelength of tryptophan,pyridoxine, NADH, or riboflavin. Furthermore, the housing may containmultiple light sources with one light source in each housing having acommon wavelength to ensure consistent particle size measurements.

In another exemplary embodiment of the invention, aparticle/fluorescence detector system uses a plurality of light sourcesfor sending light beams through a fluid to excite fluorescence of saidbiological organisms or biological agents in the fluid. The plurality oflight sources are mixed using an optical coupler or another mixingdevice. Preferably, the optical coupler modulates the plurality of lightbeams at different frequencies. A detector is positioned in the lightpath for detecting the fluorescence and particle size of said biologicalorganisms or biological agents and producing a corresponding outputsignal.

In yet another exemplary embodiment of the invention, a reflectionmechanism is placed in the path of light after the light has passedthrough a sample area containing fluid. The reflection mechanismdeflects into a second light path at least a portion of the lightscattered at a certain range of angles. A first detector is placed inthe second light path for detecting a portion of the scattered light andproducing an output signal. The first detector is preferable optimizedfor measuring particles a first size range, e.g., from 0.1 μm to 1.0 μmin size. A second detector is positioned in the light path after thereflecting mechanism for detecting a portion of the light scattered atlarger angles and producing a corresponding output signal. The seconddetector is preferable optimized for measuring particles of a secondsize range, e.g., from 1 μm to 10 μm in size.

Furthermore, in this embodiment, a wavelength selective filter or beamsplitting mechanism may be placed in said light beam after thereflection mechanism to split the beam into a plurality of light beams.In a preferred embodiment, the wavelength selective filter is a dichroicfilter. A third detector may be placed in the light path of one of theplurality of beams for detecting the fluorescence of particles in thesample area.

In another embodiment of the invention involves a test mechanism for thetesting system for a particle detection sensor including

a chamber for loading a test powder;

a filter mechanism for removing particles above predetermined sizeconnected to said chamber;

an exit of said filter is connected to a particle detection sensorsystem.

This detector system is sensitive, inexpensive, and rugged enough forfield deployment. Although the system does not necessarily always detector identify an exact particle, it can provide a sensitive and costeffective early warning of a bio-agent attack. It also can be arrangedto provide early warning of harmful airborne particles, which may casepulmonary distress, such as asbestos and beryllium dusts, or harmfulwaterborne particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the followingdetailed description of an exemplary embodiment of the invention, takenin conjunction with the accompanying drawings in which like referencenumerals refer to like parts and in which:

FIG. 1 is a schematic block diagram of the optical portion of a particledetector system according to an exemplary embodiment of the invention;

FIG. 1A shows details of the sample region portion of the detectorsystem of FIG. 1;

FIG. 2 is a graph illustrating the relationship of Mie scatteringcross-section of incident light to the airborne particle size;

FIG. 3 is a block diagram of the particle detector system according toan exemplary embodiment of the invention, incorporating the opticalsystem of FIG. 1;

FIG. 4 is a block diagram of a pulse height measurement and displaycircuit;

FIG. 5 is a schematic diagram of the analog to digital converter portionof the circuit of FIG. 4;

FIG. 5A is a diagram illustrating pulse wave forms at various points inthe circuit;

FIG. 6 illustrates an exemplary output histogram displayed by the systemof FIGS. 3 and 4 in a situation where particle counts within apredetermined size exceed a predetermined amount, triggering an alarmcondition;

FIGS. 7 and 7A are views similar to FIG. 1 of alternative forms ofparticle detectors according to the present invention in which an UV LEDis employed in place of the laser light source;

FIG. 8 is a view similar to FIG. 1 of a particle detector according toan alternative embodiment of the invention specifically designed fordetecting waterborne particles;

FIG. 9 is a view similar to FIG. 8 of a waterborne particle detectoraccording to the FIG. 8 alternative embodiment of the invention in whichan UV LED according to the FIG. 7 or 7A embodiments is employed in placeof the laser light source;

FIG. 10 is a plan view illustrating a plurality of detectors of thepresent invention in a grid;

FIG. 11 is a perspective view and FIG. 12 is a schematic view of anairborne pathogen detector and characterization system according toanother embodiment of the present invention;

FIG. 13 is a schematic block diagram of an airborne pathogen detectorand characterization system according to another preferred embodiment ofthe invention;

FIGS. 14-17 are graphs illustrating the relationship of wavelength torelative fluorescence intensity of tyrosine, tryptophan, nicotinamideadenine dinucleotide (NADH) and riboflavin; spores, road dust, ammoniumnitrate, ammonium sulfate, carbon black; saccharomyees cerevisialaerosols; and diesel exhaust, respectively;

FIG. 18 is a view similar to FIG. 12 of an airborne pathogen detectorand characterization system according to another preferred embodiment ofthe present invention;

FIG. 19 is a view similar to FIG. 18 of waterborne pathogen detectoraccording to another embodiment of the invention;

FIG. 20 is a view similar to FIG. 19 in which an UV LED is employed inplace of the laser light source.

FIG. 21 is a graph of the fluorescence emission as a function ofwavelength for NADPH;

FIG. 22 is a graph of the fluorescence emission as a function ofwavelength for riboflavin;

FIG. 23 is a graph of the fluorescence emission spectra for fourmetabolites excited by a Hg arc lamp;

FIG. 24 is a schematic of a dual excitation laser wavelength tandemmodule design of the particle/fluorescence detector system according toan exemplary embodiment of the invention;

FIG. 25 is a schematic of a the particle/fluorescence detector systemaccording to an exemplary embodiment of the invention in which two lightbeams are coupled to allow for the simultaneous measurement of twofluorescence signals;

FIG. 26A-26B are examples of optical coupler for use in theparticle/fluorescence detector system of FIG. 25;

FIG. 27 is an is a schematic of another exemplary embodiment of theinvention and an optics system to reduce noise in the light signal; and

FIG. 28 is an exemplary embodiment of a testing system for use with theparticle detector system.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1, 1A and 3 to 5 illustrate an airborne particle detector systemaccording to an exemplary embodiment of the invention, while FIG. 6illustrates an exemplary output from the system. This embodiment of thesystem is particularly intended to detect airborne or waterbornebio-terrorist agents deliberately released by terrorists or others, butmay also be used in civilian applications to detect harmful levels ofother airborne or waterborne particles which may exist naturally such asmold or bacteria, or which may have been accidentally, inadvertently,naturally, or deliberately released.

The term “fluid borne particles” as used herein means both airborneparticles and waterborne particles.

The term “collimated light” as used herein means both collimated lightand near collimated light.

The term “pathogen” as used herein refers to any airborne or waterborneparticles, biological agent, or toxin which could potentially harm oreven kill humans exposed to such particles if present in the air orwater in sufficient quantities. As used herein, “biological agent” isdefined as any microorganism, pathogen, or infectious substance, toxin,biological toxin, or any naturally occurring, bioengineered orsynthesized component of any such micro-organism, pathogen or infectioussubstance, whatever its origin or method of production. Such biologicalagents include, for example, biological toxins, bacteria, viruses,rickettsiae, spores, fungi, and protozoa, as well as others known in theart.

“Biological toxins” are poisonous substances produced or derived fromliving plants, animals, or microorganisms, but also can be produced oraltered by chemical means. A toxin, however, generally developsnaturally in a host organism (i.e., saxitoxin is produced by marinealgae), but genetically altered and/or synthetically manufactured toxinshave been produced in a laboratory environment. Compared withmicroorganisms, toxins have a relatively simple biochemical compositionand are not able to reproduce themselves. In many aspects, they arecomparable to chemical agents. Such biological toxins are, for example,botulinum and tetanus toxins, staphylococcal enterotoxin B, tricothecenemycotoxins, ricin, saxitoxin, Shiga and Shiga-like toxins, dendrotoxins,erabutoxin b, as well as other known toxins.

The detector system is designed to detect airborne or waterborneparticles within a specific size range, discriminate between biologicagents and inert or inorganic materials, and produce outputs indicatingthe number of particles of each size within the range which is detectedin a sample and indicate whether the particles are biologic ornon-biologic, and also to produce an alarm signal if the number ofparticles exceeds a predetermined value above a normal background level,and/or are biological organisms or biological agents and potentiallydangerous.

As illustrated in FIGS. 1 and 3, the first embodiment of the systembasically comprises an optical unit 10, a laser diode or other lightsource 12 directing a collimated or nearly collimated light beam intothe optical unit 10, a first photodetector 14 at the output of opticalunit detecting light transmitted through the unit, a secondphotodetector 16 for detecting the light output of the laser diode, asignal divider 18 for dividing the output of photodetector 14 by theoutput of photodetector 16, an amplifier 26 connected to the output ofdifferential amplifier 18, an analog to digital converter 22, a windowcomparator circuit 24, and a control and output display unit 25connected to the output of circuit 24. A low signal detection circuit 26is connected to the output of photodetector/monitor detector 16 whichdetects the laser diode power, and the output of circuit is alsoconnected to control unit 25. An alarm device 28 is also connected tocontrol unit 25. Control unit 25 can be a computer or custom designedhardware/software to control the system.

The optical portion 10 of the system will now be described in moredetail with reference to FIGS. 1 and 1A. A portion of this system issimilar to the optical system described in U.S. Pat. Nos. 5,986,555 and6,087,947 of Hamburger et al., the contents of which are incorporatedherein by reference. The optical system will be contained in an outerhousing 30, which may be of tubular or other shapes. The light source 12directs a collimated laser light beam 32 through an air sample region 34within the housing. When the collimated light beam 32 strikes particles35 within the air sample, a portion of the beam 36 is deflected orscattered, with the angle of deflection being dependent on the size ofthe particle. Scattered portions 36 of the light beam thereforeestablish the presence of particles within the sample. Environmental airis constantly drawn through the sample region 34 in the direction of thearrows in FIG. 1 by a fluid moving unit 37 such as a fan, in the sameway as described in the patents referenced above.

Referring to FIG. 1A, in order to ensure accurate particle detection theflow channel through the sample region 34 should be relatively small,preferably about 1 to 2 mm across. Making the flow channel too small incross section, i.e., below about 1 mm, creates too much back pressurefor accurate sampling. On the other hand, a flow channel in excess ofabout 2 mm may result in a double layer or still layer adjacent the flowchannel walls. Ideally, the flow channel will have a cross-section ofabout 1.5 to about 2.0 mm. In a preferred embodiment, the sample region34 comprises a flow cell 100 comprising a body having an inlet end 102and an outlet end 104. The inlet end 102 and the outlet end 104 eachtake the form of truncated cones which may be the same or differentshapes. A channel 106 of about 1 to about 2 mm in cross section includesan optical window 108 through which light beam 32 is directed. Channel106 connects the inlet end 102 and outlet end 104 at the apexes of thetruncated cones. Inlet 102 is open to the ambient air. Fluid moving unit37, e.g. a fan, is connected at outlet 104. In order to reduce back flowpressure one or more additional conduits 110 preferably are formedbetween the midpoint of the inlet end cone conical surface and theoutlet end cone surface to bleed air and thereby permit more uniform airfluid sampling. Preferably, the outside surface of the flow cell 100 iscoated with a metalized coating 112 which is connected to ground, inorder to obviate potential electrostatic build up.

A lens 38 is located in the housing in the path of both the unscatteredand scattered portions of the light beam exiting the sample area. Thelens 38 has a central, blocking member 40 of predetermined diameter,which is designed to absorb light. In a first exemplary embodiment,blocking member 40 comprises a black piece of vinyl adhered to the frontof lens 38, although other beam diverting devices may alternatively beused. The diameter of the blocking member 40 is such that at least theunscattered portion of the focused light beam is blocked and preventedfrom traveling any further through unit 10. The diameter of circularblocking member 40 may be about 2 mm greater than the diameter of theunfocused light beam, and may be designed such that it blocksunscattered light and light scattered by particles larger than apredetermined size, such as 50 microns. An even larger blocking membermay be used to further eliminate light scattered by particles smallerthan 50 microns, if desired. The lens may also have an annular ring (notillustrated) of light blocking material surrounding the central blockingmember 40 as described, for example, in U.S. Pat. No. 6,087,947 referredto above. This will act to block light scattered by particles smallerthan a predetermined minimum value. However, the lens and housingdiameter may alternatively be designed such that light scattered by suchparticles will not be transmitted.

In the prior patents discussed above, the beam blocking devicecomprising the lens 38 and beam blocking member 40 (and annular beamblocking ring if present) was designed to block transmission of lightscattered by particles outside a predetermined particle size range of 5to 50 microns. However, in the present invention, the particles ofinterest may have a different size range, specifically airborne mold,biological agents, or harmful dusts. Since the particles may be as smallas 1 μm or even 0.5 μm in size, the lens 38, housing 30, and beamblocking member 40 are of predetermined dimensions such that lighttransmitted by particles outside a size range of 0.5 μm to 50 μm will beblocked, while portions 42 of the light beam scattered by particleswithin the size range of 0.5 μm to 50 μm are transmitted through theannular ring portion of the lens which surrounds blocking member 40. Itwill be understood that the dimensions of the blocking member may bevaried if desired to further limit or expand the portion of the lightbeam transmitted through lens 38.

Light source 12, in addition to the focused light beam 32, alsogenerates a certain amount of noise from its surface. Such noise isfocused by lens 38 onto a circular blocking member 45 at the center ofthe second lens 44, such that it is blocked from reaching the detector14. However, the scattered portions 42 of the light beam transmitted bylens 38 are focused by lens 44 onto detector 14 as indicated in FIG. 1.Circular blocking member 45 may be identical to blocking member 40.

Beyond the previous discussed differences, optical unit 10 differs fromthe optical units described in the aforementioned two patents in thefollowing respects. First, a reflector 46 is placed on or in front ofthe beam blocking member 40. The reflector may be a tilted mirror or acoated prism set. This reflector is designed to reflect the unscattered,incident laser beam onto the second, or monitoring photodetector 16.Secondly, a transparent partition slide 47 is placed between the samplearea 34 and the beam blocking device 38, 40. The purpose of the slide isto prevent dust or other environmental pollutants from reaching theoptical elements and photodetectors. This will be particularlybeneficial when the system is used in harsh field deployment conditions.The slide is removably mounted in the housing so that it can be replacedwhen it becomes too dirty to allow sufficient light transmission, whichwill be determined by the second photodetector. Thus, the laser poweralarm may indicate either that the laser diode has lost power, or thatthe slide has become too dirty. A moderately dirty partition slide willnot affect the accuracy of particle detection, since it will reduce thelight intensity of both the unscattered portion of the light beam andthe scattered light beam, and the ratio of these two signals isrecorded.

Although the beam diverting device in the illustrated embodiment is alens having a central blocking region and optionally also an outerblocking ring, such that only light scattered in a predetermined angularregion is transmitted to the lens, the blocking device in alternativeembodiments may be a concave mirror having a central light absorbinglight blocker as above, or a central opening of predetermined diameter.The detector 14 in this case will be positioned to detect lightreflected from the concave mirror, as described in U.S. Pat. No.6,008,729 of Hamburger et al., the contents of which are alsoincorporated herein by reference. An angled mirror or prism also may beused in exactly the same way as illustrated in FIG. 1 in order to directpart of the unscattered portion of the beam onto the second detector.

The system design is based upon the principle of Mie scattering of lightby particles with sizes comparable with the wavelength of light. In theMie scattering regime, both the angular distribution and the intensityof the scattered light are strongly dependent on particle size andshape. Mie scattering is characterized by the following properties: 1)the scattered light is concentrated in the forward direction; 2) theangular distribution of the scattered light intensity is highlysensitive to the scattering particle size; and 3) the scatteringcross-section of a particle is proportional to the particle size in amonotonic but complex manner. Using visible light, such as a visiblelaser diode light output beam of wavelength 0.67 μm, the Mie scatteringmethod is ideally suited for detecting and characterizing airborneparticles in the micron size range. The relationship of Mie scatteringcross-section to particle radius is shown in FIG. 2.

The optical unit 10 of the system uses the principle that scatteringangle is proportional to particle size in order to eliminate lightscattered outside a predetermined range using a beam blocking device 36positioned in the path of light which has traveled through the sample.The remainder of the system is designed to detect the particle sizedistribution in the sample by discriminating between pulses of differentheights detected at detector 14, since the scattering cross section of aparticle is proportional to the particle size in a monotonic but complexmanner, as described above and illustrated in FIG. 2. Therefore, theheights of the electrical pulses output from detector 14 are dependenton the particle size.

The output of detector 14 is connected to one input of signal divider18, as indicated in FIG. 3, while the output of detector 16 (whichcorresponds to the laser diode output) is connected to the other inputof the signal divider 18 and the ratio of these signals is output fromthe signal divider 18. FIG. 4 is a block diagram of the pulse heightmeasurement circuit, making up the converter unit 22, the windowcomparator unit 24, and the control and output display unit 25 in anexemplary embodiment of the invention, while FIG. 5 is a schematicillustrating the digital converter unit in more detail. The output ofthe photodetector will be a pulse signal, for example a signal 60 asillustrated in FIG. 4, of a series of analog pulses, with each pulserepresenting right scattered by a particle in the air sample, and theheight of the pulse being proportional to the particle size. Eachincoming pulse from the photodetector passes a high pass filter 62 inorder to eliminate the DC background, and then goes through a buffer 64to a peak detector 65 which will measure the height of the incomingpulse. The output of peak detector 65 will be a series of pulse countingsignals with pulse height data. One example of a suitable analog todigital converter and peak detector circuit is illustrated in moredetail in FIG. 5, with FIG. 5A illustrating pulse outputs at variouspoints in the circuit. The output signal “PEAK OUT” in FIG. 5A is sentto the window comparator unit for classification. The other pulsesillustrated in FIG. 5A are timing and enabling signals to tell thewindow comparator to take and store the count.

The window comparator unit has a series of window comparators 66(labeled 1-10 in FIG. 4 by way of example) each designed to detectpulses in a predetermined voltage range (window voltage). Each windowcomparator 66 will send a signal to its associated digital counter 68only if the incoming pulse height is within its window voltage (e.g. 5mV to 7.5 mV for comparator #5). The outputs of the counters 68 areconnected to a display panel 70, which will display particle numbers ineach particle size, bin. Thus, the output display unit 25 may comprise abar graph lit by light emitting diode (LED) arrays, with the LEDs beinglit up in sequence for each particle size based on input from theassociated counter, to produce a histogram of the particle sizedistribution. The bar graph may be in different colors for the differentparticle sizes. The outputs may also, or alternatively, be connected toa computer programmed to display a histogram of the particle sizedistribution on its display screen.

The window comparator unit 24 has a plurality of comparators 66 andcounters or bins 68 for counting pulses corresponding to particle sizesin the range of interest. In FIG. 4, ten such bins are shown. However,fourteen bins may be provided for particle sizes from one to sevenmicrons, at a 0.5 micron spacing. A smaller or greater number ofcomparators and counters may be provided if a smaller or larger sizerange is required, for example a more limited pathogen size range of 1to 5 μm. FIG. 6 illustrates an example of a histogram of particle sizedistribution. Although this indicates a distribution in the range from 1to 19 μm, it will be understood that the control unit may be programmedto display a particle size distribution histogram over the smaller rangeof 1-7 cm as discussed above or any desired range. The output of controlunit 25 may also be connected to a visible and/or audible alarm device28, such as an alarm light on the front of the housing and a buzzer orthe like.

Any suitable software may be used to generate the output displayhistogram, such as LabView software available from National InstrumentsCorporation of Austin, Tex. This software may also be used to produce anoutput to activate an audible alarm 28 if the number of counts in a sizerange corresponding to a pathogen or bio-agent particle size exceeds apredetermined level above the normal ambient level. This will help toreduce or even eliminate false alarms. The output of the computer mayalso be used to trigger a more elaborate bio-agent detection device,such as a PCR based anthrax detection apparatus. This combinationdetection scheme will be cost effective and will further reduce the riskof a false alarm.

In a modified arrangement of the invention, the histogram of theairborne particle size distribution may be compared to that of knownweaponized bio-agents, since the processing procedure for such agents isknown to have a signature size distribution unique to the machinery usedin the process. Thus, the detector system of this invention can provideforensic information on the possible origin of the bio-agentmanufacturer.

As noted above, the most probable bio-agents for use in a terroristattack have size ranges from 1 μm to 7 μm. Table 1 below shows thecharacteristics of Category A bio-terrorist agents, as specified by theCenter for Disease Control: TABLE 1 Category A bio-terrorist agent AGENTSIZE CHARACTERISTICS Bacillus Anthracis Rod shape: width 1.0-1.2 μm,length 3.0-5.0 μm (spore 1.0 × 1.5 μm) Yersinia pestis Oval 1.0-2.0 μm(plague) Clostidium botulinum Rod shape: width 0.8-1.3 μm, length4.4-8.6 μm Francisella tularensis Rod shape: width 0.2 μm, length 0.7 μm

There exists in environmental air only a very small and constantconcentration of naturally occurring airborne particles in the sizerange of about 1 μm to 7 μm. The particle size ranges of smog incursionin metropolitan areas and sudden growth of local dust source are peakedat 0.3 μm and 5 μm, respectively. Pollens and other allergens can alsobe present in the air during blooming seasons, and the size range ofallergen particulates is from about 5 to 50 μm. Thus, few of thesenaturally occurring airborne particles are in the typical size range ofweaponized bio-agents (1 to 7 μm). In addition, while mold may have aparticle size of about 1 to 5 μm, the amount of mold particles in theair in any particular location generally does not vary suddenly. Thedetector system of this invention is therefore designed to detectparticles in this specific size range and produce an output representingthe range of particle sizes detected at 0.5 μm intervals. Any sudden andlocalized increase in the number of airborne particles within a 1 to 7μm size range most likely signifies an intentional release of hostilebio-agents or pathogens. The system can be set up to detect and store anatural background level of particles within the size range of interest,and then use this as a comparison level for subsequent outputhistograms, in order to activate the alarm on detection of a suddenincrease. The particle size distribution histogram of FIG. 6 indicates aprobable hazardous situation where the number of particles detected inthe size range of 1 to 7 μm is way over normal levels.

Although the particle detector system as above described will notidentify the particular particle, it will serve as a sensitive andcost-effective warning of an airborne bio-agent attack because of therelative scarcity of airborne particles in the range of interest innormal meteorological conditions. Particles within this range canpenetrate the human lungs and could be potentially harmful or even fatalfor those inhaling them. The alarm provides a warning for individuals inthe vicinity to evacuate the area immediately, reducing the exposure tosuch agents.

The same detection system and method can also be used to detecthazardous levels of potentially harmful dusts in manufacturingfacilities. For example, harmful asbestos fibers are in the size rangeof about 5 μm, having a typical length of about 5 μm or longer and adiameter of about 1-2 μm. Beryllium dusts are also, harmful whenbreathed into the lungs, which will happen if they are in the 1-5 μmrange. The detection system of this invention could be provided inbuildings containing asbestos, or when workers are working in suchbuildings, to provide a warning signal when an unusual spike in the 1 to5 μm range is detected, which may indicate harmful levels of asbestosfibers in the air. Similarly, the detector may be used in the vicinitywhen workers are machining beryllium parts, in order to give a warningsignal if the number of particles in the 1 to 5 μm size range suddenlyincreases, indicating the possible presence of harmful levels ofberyllium dust. Even though the detector cannot differentiate asbestosor beryllium dusts from non-harmful particles in the same size range,any sudden increase in detected particle levels in this size range whenworking with asbestos or beryllium will provide an indication of apotentially hazardous situation requiring evacuation of the area andfurther testing.

In the detector system described above, a two stage detection anddiscrimination process is used, with the optical portion 10 of thesystem first eliminating light scattered outside a predetermined angularrange incorporating the particle size range of interest. Subsequently,detected output pulses are discriminated according to pulse height, thenumber of pulses of each height are counted and converted to particlesize within, e.g., 0.2 μm, and the results are displayed as a histogram,with a new histogram being generated at suitable time intervals toillustrate changing particle distribution conditions. However, insteadof displaying a particle size distribution histogram, the opticalportion of the detector apparatus may alternatively be arranged todirect only that part of the scattered light signal corresponding to aparticle size range of 1 to 7 μm to the detector 14, and the remainderof the system is then arranged to emit an alarm signal if the output ofthe detector exceeds a predetermined threshold level. This will providea less accurate output, and does not provide any discrimination ofparticle sizes within the detected size range, but can still give arelatively accurate warning of the presence of an unusually large numberof particles within a size range corresponding to known airbornepathogens allergens or other harmful particles, e.g., beryllium dust orasbestos. The optical assembly 10 of FIG. 1 would only have to bemodified to provide a larger central blocking area to block lightscattered by particles having a size greater than about 7 μm, and theoutput circuitry would be modified to provide a threshold leveldiscriminator at the output of the detector, and to provide an outputsignal from the discriminator to activate an alarm if the detectedsignal is above the selected threshold.

The pathogen detector of this invention can be used in variousapplications. For example, it may be implemented as a battery powered,portable, hand-held detector for field personnel. In such case, an outerhousing may hold both the optical unit as well as the electricalcircuitry to count particles by size range, and will have a display ofthe current particle counts for each particle size, such as an LEDdisplay. It also may incorporate a transmitter for sending radio signalsto a base station. It may also incorporate an audible alarm and awarning light for laser low power condition. A stand-alone, desk topversion may also be provided for use in office buildings or the like.This will be similar to the field version, but will be powered from astandard electrical wall socket via an AC/DC converter. In the lattercase, the detector may be used to provide protection from bio-agentcontaminated letters or packages in office desk top settings.

The detector also may be part of a multiplexed system for buildingsecurity, comprising a number of detectors in different rooms linked toa central monitoring computer or control station. The control stationcan be programmed to monitor the particle counts from each room, and toanalyze the origin of any unusual increase in pathogen-size particles,and to predict the potential spread pattern within the building. Largergrid systems may be used in large building complexes, such as militarybases or city blocks, i.e., as illustrated in FIG. 10. The detectors maybe hard wired, or may have radio transmitters for transmitting data to acentral control station which again can analyze the origin of anydetected increase in potential bio-agent particles, and the potentiallyspread of any bio-agent plume.

The airborne particle detector of the present invention alsoadvantageously may be used to monitor clean room facilities forpotential contamination and/or material loss.

In another embodiment of the invention, an LED is employed as the lightsource in place of the laser diode. Using an LED as the light source hasadvantages over a laser including longer lifetime, lower device cost,and reduced speckle. The electronic requirements and shieldingrequirements for LEDs also are less stringent than that for lasers.However, an LED is a relatively diffuse light source with a lightemission angular distribution typically much larger than that of a laserdiode. Accordingly, when an LED is used additional optics are necessaryto focus and collimate the light beams. FIG. 9 shows an optical unit, anLED light source 120 and optical lens 122 instead of a laser. FIG. 7illustrates a simplified optical path using an LED 120 as the lightsource in an airborne particle detector in accordance with the presentinvention. As seen in FIG. 7, an optical lens assembly 122 is placed infront of the LED light source 120 between the LED 120 and the flow cell100. Optical lens assembly 122 comprises a plurality of lenses whichtogether shape the light beam from the LED 122 into a near-collimatedlight beam 124 which is concentrated on the flow cell 100.Alternatively, as shown in FIG. 7A, the optical lens 126 may be designedto focus the light beam 128 on or near the first lens 38 of the Miescattering particle size detector which is similar to the Mie particlesize detector discussed previously. Various LEDs are availablecommercially that emit over a desired wavelength range andadvantageously may be employed an in airborne particle detector of thepresent invention.

Other embodiments are possible. For example, referring to FIG. 8, theabove described airborne particle detector may be modified for use fordetection of waterborne particles by providing water tight inlet andoutlet couplings 140, 142 at the inlet and outlet ends of the samplecell 34, and a peristaltic or scroll pump 144 in place of the fan 37.Since waterborne particles of interest, i.e., bacteria or bacterialspores may have a size range of about 1 to 20 μm, the dimensions of beamdiverting member 40 should be adjusted accordingly.

Referring first to FIGS. 11, 12 and 13, the system for detection andidentification of airborne or waterborne biological agents fluorescencein accordance with an additional embodiment of the invention comprises afirst optical unit 210 for detecting particles of a selected particlesize, e.g., approximately 1 to 7 microns, and a second optical unit 300for discriminating between biological toxins or biological agents andinorganic particles. The first optical unit 210 comprises a laser diodeor other light source 212 for directing a light beam into the opticalunit, a first photodetector 214 at the output of optical unit fordetecting light transmitted through the unit, a second photodetector 216for detecting the light output of the laser diode, a differentialamplifier 218 for dividing the output of photodetector 214 by the outputof photodetector 216, an amplifier 226 connected to the output ofdifferential amplifier 218, an analog to digital converter 222, a windowcomparator circuit 224, and a control and output display unit 225connected to the output of circuit 224. A low signal detection circuit226 is connected to the output of photodetector 216 which detects thelaser diode power, and the output of circuit 226 is also connected tocontrol unit 225. An alarm device 228 is also connected to control 225.The sample region in this exemplary embodiment is the same as previousdescribed for other embodiments with reference to FIG. 1A.

Referring in particular to FIGS. 11-13, the second optical unit 300includes an excitation laser 212 operating in a wavelength of a selectedwavelength range, e.g., about 370 nm to about 410 nm. Laser 212 directsa collimated laser light beam 232 through the air sample region 234within the housing. Laser 212 should be sufficiently intense (withfluence of, for example, about 0.03 Joules/cm²) to excite measurablefluorescence in single particles that contain even only a few picogramsof material. When the collimated light beam from laser 212 strikesbiological particles within the air sample, if the particles contain abiological material such as, for example, riboflavin, and/or NADH, theparticles will exhibit a fluorescence signal, which is collected via anelliptical mirror 306 located surrounding region 234, in part, andfocused onto a fluorescence detector 302. Laser 212, mirror 306, anddetector 302 are all fixedly positioned to the housing. The choice ofelliptical mirror is made by considering its ability to focus lightemanating from one of the foci onto the other one. In thisconfiguration, the elliptical mirror serves as an efficient collector offluorescence light from the bio-aerosol (at the first focal point of theellipsoid) for a photo-detector located at the second focal point of thesame ellipsoid. A parabolic mirror or other reflective element alsocould be used.

In a preferred embodiment of the invention, the alarm will be activatedonly after two conditions are met: (1) a sudden increase in the numberof airborne particles within a predetermined size range (about 1 toabout 7 nm) is detected; and (2) biological organisms or biologicalagents or organic materials are detected using, e.g., laser inducedfluorescence as described below.

By themselves, particle size sensors are vulnerable to false alarms fromambient particulates. To further reduce these false alarms, the pathogendetector system of this embodiment is a biological organism orbiological agent verification detector combining the particle sizingcapability with an UV light-induced fluorescence sensor to discriminatebetween biological and non-biological particles. The pathogen detectorsystem of the present invention also preferably includes a secondoptical unit 300 which includes a laser induced fluorescent sensor todetect metabolites which are present in biological organisms orbiological agents, including biological warfare agents. Moreparticularly, the second optical unit 100 includes an excitation laseroperating in a wavelength of about 270 nm to about 410 nm, preferablyabout 370 nm to about 410 nm. A wavelength of about 270 nm to about 410nm is chosen based on the premise that bio-agents comprise three primarymetabolites: tryptophan, which normally fluoresces at about 270 nm witha range of about 220 nm-about 300 nm; nicotinamide adenine dinucleotide(NADH) which normally fluoresces at about 340 nm (range about 300nm-about 400 nm); and riboflavin which normally fluoresces at about 400nm (range about 320 nm-about 420 nm). Preferably, however, we prefer touse an excitation laser with a wavelength of about 370 to about 410 nm.This ensures excitation of two of the three aforesaid primarymetabolites, NADH, and riboflavin in bio-agents, but excludes excitationof interference such as diesel engine exhaust and other inert particlessuch as dust or baby powder. Thus, in a preferred embodiment the presentinvention makes a judicial selection of wavelength range of theexcitation light source, which retains the ability of excitingfluorescence from NADH and riboflavin (foregoing the ability to excitetryptophan) while excluding the excitation of interferents such asdiesel engine exhaust. This step is taken to reduce false alarmsgenerated by diesel exhaust (which can be excited by short UVwavelengths such as 266 nm light).

The output from fluorescence detector 302 is connected to a divider 219which in turn is connected via an amplifier 227 and A/D converter 222 tocontrol 225 which in turn is connected to display and alarm 228.

As in the case of the previously described embodiment, the pathogendetector may be implemented as a battery powered portable, hand-helddetector for field personnel, and include a display for the currentparticle counts for each particle size and for signaling whenfluorescencing metabolites are detected. It may also incorporate anaudible alarm and a warning light for laser low power condition, and, ifdesired, a transmitter for sending signals to a base station. Astand-alone, desk top version may also be provided for use in officebuildings or the like. This will be similar to the field version, butmay be powered from a standard electrical wall socket via an AC/DCconverter. In the latter case, the detector may be used to provideprotection from bio-agent contaminated letters or packages in officedesk top settings.

This embodiment of the invention is susceptible to modification. Forexample, a single laser source operating at a wavelength of about 370 nmto about 410 nm may be employed with an optical splitter in place ofseparate light sources for particle size count and fluorescenceexcitation. In addition, the invention may be employed as a fluorescenceparticle sizing biosensor for waterborne pathogen detection. Waterbornepathogens may be either bacteria or bacterial spores. Accordingly, thesize range of waterborne pathogens is somewhat wider than for airbornepathogens, typically from about 1 to about 20 microns.

Referring to FIGS. 19 and 20, the device which is similar to the deviceof FIG. 11 may be modified for use for waterborne pathogen detection byproviding water tight inlet and outlet couplings 340, 342 to the sampleregion 234, and a peristaltic or scroll pump 324.

In previous embodiments, an optical system with a sensing fluorescenceemission detector is used to analyze metabolites. Microbes (bacteria,fungi etc) contain certain chemical compounds (metabolites) involved inmetabolism. Tryptophan, pyridoxine, NADH, and riboflavin are among themajor metabolites in microbes. Since these different metabolites havedifferent excitation wavelength ranges from optimal excitation, it isadvantageous to have a scheme for employing multiple lasers withdifferent excitation wavelengths. The following are rationales for themultiple wavelength scheme: 1) to optimize the excitation efficiency bytargeting the maxima of different metabolites fluorescence excitationcurve; 2) since different types of bacteria (or other microbes) havedifferent ratios of composition of metabolites in their cells, themultiple wavelength excitation will be able to get the information aboutthe relative compositions of the metabolites and enable us to do acoarse classification of the types of microbes.

In order to have unambiguous analyses of the fluorescence emission fromdifferent metabolites in another preferred embodiment of the invention,a tandem modular design is used, in which a stream of particles passesthrough two fluorescence sensors 500, 502 (see FIG. 24) in tandem. Eachsensor has a laser 510, 512 with different wavelengths (tuned to optimalexcitation wavelength of various metabolites). As an example of thepreferred embodiment: 405 nm laser wavelength is suitable forriboflavin, and 330-380 nm laser wavelength range is optimal for NADH.Two modules of the fluorescence sensors as shown in FIG. 24 (sensor 500and sensor 502 having laser wavelengths of 405 nm and 340 nmrespectively) are placed in series with a common airflow tube 504, whichpasses through the particle sensing regions 506, 508 of both sensors.Sensor 500 and sensor 502 will optimally detect the presences ofriboflavin and NADH respectively. FIGS. 21-22 show the fluorescenceemission verses excitation wavelength curve shown from: J.-K. Li et al,“Monitoring cell concentration & activity by multiple excitationfluorometry” Biotechnology. Prog. Vol. 7, 21, 1991.

Alternatively, for optimal excitation of fluorescence from tryptophan orpyridoxine, the wavelength selection will be at 270 nm and 320 nmrespectively.

The fluorescence detection of sensor 500 (or sensor 502) can be of thefollowing types: 1) integrated overall fluorescence signal in the wholespectral range. In this case, the fluorescence signal from themetabolite will be sent to the photo-detector of the sensor afterpassing through a long-wavelength optical pass filter to eliminate theexcitation laser light. The ratio between the signal strengths of sensor500 and sensor 502 will indicate the relative abundance of two types ofmetabolites in each sensor. (For example, if 405 nm and 340 nmwavelengths are chosen for the two sensors, then the ratio of theoverall fluorescence signals will be related to the relative abundanceof riboflavin and NADH.) 2) Wavelength-selective elements in individualsensor do spectral analysis. In this case, the spectral analysesprovided by two sensors will provide the fluorescence spectralinformation under different conditions of excitation (i.e. differentwavelengths). In either case, the information gathered will be useful inclassifying the microbes.

FIG. 23 shows the fluorescence emission spectra of aforementioned fourmetabolites. Spectral analyses, especially those with differentexcitation wavelength, will enable the probing of the composition ofmicrobes and use the resultant information for the purpose of microbialdetection and classification.

The schematic of the sensor with two chambers is shown in FIG. 24.Design considerations for the multi-wavelength pathogen sensorinclude: 1) each sensor unit in the tandem configuration is aself-contained fluorescence/particle size sensor with a specificwavelength optimized to a target metabolite compound. 2) Two sensors500, 502 share the same airflow tube or passageway 504, as shown in FIG.24. The airborne particles in the airflow pass 504 through the sensingregion 506, 508 of the sensors in sequence. The two sensors 500, 502measures the same batch of airborne particles in a serial manner, it istherefore desirable to correlate the fluorescence signals from thesestwo sensors. One way to do this correlation is to use particle sizemeasurement data from both sensors to pair up the fluorescence signalsfrom two sensors, under the assumption that in the short time period forparticles to transport from sensor 500 to sensor 502 the distribution ofparticle sizes is not significantly changed. 3) As a variation of thecurrent fluorescence/particle size sensor design, two lasers might beused in each sensor: a laser common to sensor 500 and sensor 502 (e.g. ared 630 nm laser diode) is used to do particle size measurement toensure a uniform way of determining particle size whereas an excitationlaser (different one for sensor 500 and sensor 502 respectively) is usedto excite fluorescence from metabolites. The reason for using a commonlaser wavelength for both sensors is to ensure a consistent particlesize measurement so that the fluorescence signals from these two sensorscan be correlated correctly based on the particle size information. Thisarrangement is to avoid the possibility of skewing the size measurementby the different absorption of the excitation light by the particles.While this exemplary embodiment uses two sensors and housings, a personskilled in the art would understand any number of housings or sensorsmay be used.

In yet another embodiment of the present invention, two light beams arecoupled to allow for the simultaneous measurement of two fluorescencesignals. As shown in FIG. 25, two light sources 802, 804 are coupledthrough a optical coupler 812. The coupling can be done using either afiber coupler 840 or a beam splitter 842, as illustrated in FIG. 26. Thetwo combined light beams 814 intercept the incoming particles in thenozzle window opening 818 in the optical unit 816.

The two light sources 802, 804 are modulated at two distinct electricalfrequencies (f1 and f2) by modulation units 820, 822. The modulationunits 820, 822 can be achieved by internal electrical current modulation(if the two sources are, e.g., LED's or laser diodes) or externalmodulation by a mechanical chopper, an acousto-optical modulator or anelectro-optical modulator.

In a preferred embodiment, a photomultiplier tube (PMT) 824 is used todetect fluorescence signals in the optical unit 816. The signal 826 outof the PMT is routed to two lock-in amplifiers 828, 830 tuned torespective modulation frequency (f1 or f2). In this scheme, the signalwith modulation frequency f1 is originated from excitation wavelength λ1and the signal with modulation frequency 12 is originated fromexcitation wavelength λ2. With differently modulated incident lightbeams and corresponding lock-in amplifiers, although the fluorescencesignals from two excitation sources are mixed optically, they havedifferent modulation frequencies (f1 and f2 respectively), thereforethey are electronically distinct and readily differentiable by the twolock-in amplifiers 828, 830. The two signal outputs from lock-inamplifiers 828, 830 are FLOUR1 and FLOUR2 respectively.

Likewise, at the optical coupler, a portion of the beam is split off andsent to a photodetector 832. The photodetector 832 converts the light toa current signal and then an amplifier 834 such as a trans-impedanceamplifier (TIA) converts the current signal to a voltage signal.Amplifiers 836, 838 finally selectively amplifies the signal having aspecific modulating frequency to create REF1 and REF2 signals. The REF1and REF2 signals are then subtracted from the FLOUR1 and FLOUR2 signals,respectively, to create the fluorescence emission spectra for theparticles in the sample.

Another embodiment of the invention involves modifying theflorescence/particle size detector system based on simulations andexperiments on the beam blocker in the fluorescence/particle sizesensor. Previously patents and patent applications by Hamburger et al.have disclosed the use of a beam blocker to block the residual portionof the laser from interfering with the measurement of the scatteredlight from the particles.

In this embodiment of the present invention, different sizes of beamblockers are used to improve sensitivity of the fluorescence/particlesize detector system. When the beam blocker size is increased, all theparticles that would have been seen otherwise are still viewable, onlywith a reduced intensity. The beam blocker may be enlarged to blocknearly the whole lens without significant reduction in the ability tomeasure particle over a wide range of sizes.

Furthermore, light scatter by the beam blocker can be collected andmeasured. For a very small beam blocker, the correlation between thescatter light and the particle size does not fit a simple relationshipand was even non-monotonic under certain conditions. However, for acertain angle, the blocker reduced these inconsistencies and provided avery predictable relationship between particle size and collectedscattered light. In addition, as the angle is increased the relationshipremains basically unchanged except for a reduction in the amount oflight collected. That is, the blocker tolerances are very relaxed aslong as the blockers are larger than a minimum size and the relationshipbetween particle size and collected light was highly predictable. Thisrelationship between the particle size to the collected scatter lightfor larger beam blockers was fairly smooth and predictable, even with 10and 20 μm particles. Therefore, placing a second detector in chamber tocollect the light reflected off the beam blocker allows for anothermeans of detecting the particle size.

Use of second detector is most advantageous in measure particle of thesize 0.1 μm to 10 μm. Test and simulations have shown that the dynamicrange needed measure particle down to 0.1 μm size along with the largerparticle would require a dynamic range for the detectors that is hard toachieve. Blocked light could provide better sensitivity for measuringsmall particles and tests have shown an ideal point into which thebreak-up of the angular range of particles measured across the lens.

In this embodiment, the fluorescence/particle size detector system 900does not have a beam blocker per se. However, as in previousembodiments, the light beam 906 enters the sample region 904 within thehousing 902 and the beam is deflected off particles in the fluid flow. Alens 908 is located in the housing in the path of both the unscatteredand scattered portions of the beam exiting the sample area 904. Ablocking section 910 is placed behind the lens 908 to reflect, into lowangle detection unit 912, the unscattered portion of the beam and theportion of light scattered at a low angle The low angle detection unit912 includes a detector and optics to focus the beam and remove theunscattered portion of the beam before the beam enters the detector. Thelower angle detector may be optimized to measure particles from 0.1 μmto 1 μm.

The housing 902 also contains a fluorescence detector 914 and a particledetector 916. A wavelength selective filter 912 such as a dichroicfilter is positioned in path of the light beam behind the blockingsection 910. The filter 912 selectively transmits light to thefluorescence detector 914 and the particle detector 916 through lens918, 920 respectively. The particle detector 916 may be optimized tomeasure particles in the range of 1 μm to 10 μm or larger. By breakingup the ranges of particles and scattered intensities any one detectormeasure, the dynamic range needed for the detectors is reduced to a moreachievable range.

This embodiment also includes optics to reduce the noise in the laser.These optics may be used with any embodiment of the invention. Theresidual noise reducing optics includes: a notch filter 922; a beamexpander 924; a linear polarizer 926 and a top hat filter 928.

This concept of using multiple detectors can be extended to selectingarbitrary angular regions of the collecting lens to be redirected toseparate detectors that correspond to an optimized region of particlesizes to detect. The limit of this would be using a camera to collectall the light and analyze the resulting image. Such an extreme isimpractical, as the camera is much slower than individual detectors,requires more processing power, and is significantly more costly toimplement. By keeping these zones to a minimum and comparing additionalinformation like the intensity for the individual polarizations and thescattering at multiple wavelengths, it may be possible to achieveincreased and new sensitivities.

Yet another embodiment of the current invention involves an improvedtesting system for the fluorescence/particle size sensor. To test theability of the system to detect micron size particles, a test powdercontaining micron size particles must be injected into the sample region34, as shown in FIG. 1. Traditionally, test powder is placed in achamber and connected to the sample region 34. Air is then blown throughthe chamber to force the test particles to aerosolize and push theparticles into sample region of the fluorescence/particle size sensor.

Typically, Arizona Road Dust is used for these tests. Arizona Road Dusthas been used for testing filtration, automotive, and heavy equipmentcomponents for decades. A variety of names have been applied to ArizonaRoad Dust including Arizona Silica, AC Fine and AC Coarse Test Dusts,SAE Fine and Coarse Test Dusts, J726 Test Dusts, and most recently ISOUltrafine, ISO Fine, ISO Medium and ISO Coarse Test Dusts. Arizona RoadDust consists of refined material that has settled out of the air in theSalt River Valley, Ariz. Examination of air floated dust particles fromthe Salt River Valley of Arizona reveals that it contains a highpercentage of extremely fine particles, which are highly abrasive innature and thus a good testing substitute for airborne pathogens,microbes, molds, biological warfare agents and dangerous dust. However,Arizona Road Dust and its alternatives have a tendency to clump togetherinto large particles and interfere with testing and calibration of thedetection system. Thus, a need exists for a system that limits theclumping of larger particles entering the sensor during testing andcalibration.

In this embodiment of the test system, a particle size filter unit 700is provided to the eliminate the problem of larger particles or clumpsof particles entering the fluorescence/particle size detection system. Aquantity of test powder 702 is placed on a filter medium 708, and thefilter 700 is tapped in order to drive the particles into and throughthe filter into chamber 706 as shown in FIG. 28. The outlet end 710 ofthe chamber 706 is connected to the inlet end 102 of the sample region34 from FIG. 1A. (See FIGS. 1 and 1A). The filter medium restricts thelarge unwanted particles or clumps of smaller particles from beingdelivered to the inlet 102 of the particle detector system.

The filter unit 700 comprises a size selective filter medium 708.Preferably, the filter medium 708 is a High Efficiency Particulate Air(HEPA) Filter. HEPA filters are required to remove 99.97% of 0.3 micronsparticles from the air. Thus, they are ideally suited for use in thetesting system for the fluorescence/particle size detection system.However, the filter medium used is not limited to any one type offilter. Any filter medium that removes particles or clumps of particleabove the minimum requirements of user is consistent with thisembodiment of the invention.

It should be emphasized that the above-described embodiments of thepresent invention are merely possible examples of implementations,merely set forth for a clear understanding of the principles of theinvention. Many variations and modifications may be made to theabove-described embodiment(s) of the invention without departingsubstantially from the spirit and principles of the invention. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and the present invention and protected bythe following claims.

1. An airborne particle detector system, comprising: an outer housinghaving an air sample cell area of cross-section not in excess of about 2mm; a light source on one side of the air sample cell area for sending afocused beam of light through the sample air, whereby portions of thebeam of light are scattered at various angles by particles of varioussizes present in the sample area, and an unscattered portion of the beamof light remains unscattered; a beam blocking device on the oppositeside of the air sample cell area for blocking at least the portion ofthe unscattered portion of the beam of light; a first detector withcontrol circuitry positioned in the light path after the beam blockingdevice for detecting a portion of the scattered light, and producing anoutput including information on the number of particles in the lightpath within a predetermined size range.
 2. The system claims in claim 1,further comprising one or more of the following features: (a) an alarmunit for providing a warning signal if the number of particles within apredetermined size range exceeds a predetermined normal level withinthat size range, and preferably wherein the alarm unit produces an alarmsignal if the number of particles detected within a size range ofapproximately 1 to 7 μm exceeds a predetermined level. (b) a processingunit connected to the output of the pulse height discriminator forprocessing the particle size distribution at a given time, based on theheight of each pulse, producing a histogram of the airborne particlesize distribution, and displaying the histogram on an output device; (c)a reflector positioned in front of the beam blocking device in the pathof the unscattered portion of the light beam for reflecting at leastpart of the unscattered portion in a second light path, and a secondphotodetector positioned to detect light reflected from the reflector,and/or preferably including a power monitor connected to the output ofthe second photodetector for detecting decrease in light source outputpower, and an alarm device connected to the power monitor for producingan alarm signal if the light source power falls below a predeterminedlevel, and/or preferably a differential amplifier connected to theoutputs of the two photodetectors for dividing the output of the firstphotodetector by the output of the second photodetector, thedifferential amplifier having an output connected to the pulse heightdiscriminator. (d) a transparent partition slide positioned between thesample area and the beam blocking device, and preferably wherein thepartition slide is removably mounted in the housing; (e) the lightsource comprises a laser; (f) the light source comprises an LED andpreferably also includes optical lens for shaping light from said LEDinto near collimated light; (g) wherein said light source includesoptical lens for shaping light and/or removing noise from said lightbeam.
 3. An airborne particle detector system, comprising: an outerhousing having an air sample cell; a light source on one side of the airsample cell area for sending a focused beam of light through the sampleair, whereby portions of the beam of light are scattered at variousangles by particles of various sizes present in the sample area, and anunscattered portion of the beam of light remains unscattered; a beamblocking device on the opposite side of the air sample cell area forblocking at least the portion of the unscattered portion of the beam oflight; a first detector positioned in the light path after the beamblocking device for detecting a portion of the scattered light, andproducing output pulses in which each pulse has a height proportional toparticle size; and a pulse height discriminator for obtaining the sizedistribution of airborne particles detected in the air sample at a giventime.
 4. The system claims in claim 3, further comprising one or more ofthe following features: (a) an alarm unit for providing a warning signalif the number of particles within a predetermined size range exceeds apredetermined normal level within that size range, and preferablywherein the alarm unit produces an alarm signal if the number ofparticles detected within a size range of approximately 1 to 7 μmexceeds a predetermined level; (b) a processing unit connected to theoutput of the pulse height discriminator for processing the particlesize distribution at a given time, based on the height of each pulse,producing a histogram of the airborne particle size distribution, anddisplaying the histogram on an output device; (c) a reflector positionedin front of the beam blocking device in the path of the unscatteredportion of the light beam for reflecting at least part of theunscattered portion in a second light path, and a second photodetectorpositioned to detect light reflected from the reflector, and preferablyincluding a power monitor connected to the output of the secondphotodetector for detecting decrease in light source output power, andan alarm device connected to the power monitor for producing an alarmsignal if the light source power falls below a predetermined leveland/or preferably a differential amplifier connected to the outputs ofthe two photodetectors for dividing the output of the firstphotodetector by the output of the second photodetector, thedifferential amplifier having an output connected to the pulse heightdiscriminator; (d) a transparent partition slide positioned between thesample area and the beam blocking device, and preferably wherein thepartition slide is removably mounted in the housing; (e) the lightsource comprises a laser; (f) the light source comprises an LED; andalso preferably includes optical lens for shaping light from said LEDinto near collimated light; (g) wherein said light source includesoptical lens for shaping light and/or removing noise from said lightbeam.
 5. A detector apparatus for detecting airborne particles in a sizerange of approximately 1 to 7 μm in environmental air, comprising: alight source for directing a focused beam of light through a sample ofenvironmental air in a sample cell of cross-section not in excess ofabout 2 mm, whereby a first portion of said light beam remainsunscattered and a second portion of said light beam is scattered atvarious angles by particles of various sizes present in the air sample,the scattering angle and scattering cross-section being dependent on theparticle size; a beam separating device for separating a predeterminedpart of the light beam corresponding to light scattered by particleswithin a predetermined size range from the remainder of the light beamand directing the separated part of the light beam along a light path;and a first detector positioned in the light path for detecting saidseparated part of the light beam and producing a corresponding outputsignal including information on the number of particles in the lightpath within a predetermined size range.
 6. The system as claimed inclaim 5, comprising one or more of the following features: (a) a controlunit connected to the detector output for generating an alarm signal ifthe detected number of particles within a range of approximately 1 to 7μm in size exceeds a predetermined value; (b) a pulse heightdiscriminator connected to the output of the detector for separating andcounting output pulses from the detector based on pulse height, aprocessing unit connected to the output of the pulse heightdiscriminator for processing the particle size distribution at a giventime, based on the height of each pulse, and producing an outputcomprising a histogram of the airborne particle size distribution, and adisplay device connected to the output of the processing unit fordisplaying the particle size distribution histogram; (c) a reflectorpositioned in front of the beam separating device in the path of theunscattered portion of the light beam for reflecting at least part ofthe unscattered portion in a second light path, and a secondphotodetector positioned to detect light reflected from the reflectorand preferably including a power monitor connected to the output of thesecond photodetector for detecting decrease in light source outputpower, and an alarm device connected to the power monitor for producingan alarm signal if the light source power falls below a predeterminedlevel, and/or preferably a differential amplifier connected to theoutputs of the two photodetectors for dividing the output of the firstphotodetector by the output of the second photodetector, the output ofthe differential amplifier having an output connected to the pulseheight discriminator; (d) a reflector positioned in front of the beamseparating device in the path of a part of the scattered portion of thelight beam for reflecting at least part of the scattered portion in asecond light path, and a second photodetector positioned to detect lightreflected from the reflector; (e) a transparent partition slidepositioned between the sample area and the beam separating device; (f)the light source comprises a laser; (g) the light source comprises anLED and preferably optical lens for shaping light from said LED intonear collimated light.
 7. A method of detecting airborne particles,comprising the steps of: directing a light beam through a sample ofenvironmental air in a sample cell of cross-section not in excess ofabout 2 mm such that a first portion of the light beam is scattered byparticles present in the sample and a second portion remainsunscattered; receiving both portions of the light beam which have passedthrough the air sample and directing the light beam portions onto a beamblocking device; blocking at least the second portion of the light beamat the beam blocking device and directing at least part of the firstportion of the light beam onto a first detector; measuring the pulseheight of electrical pulses output from the first detector; counting thenumber of pulses of each pulse height in a predetermined time intervaland converting the pulse heights to particle sizes.
 8. The method asclaimed in claim 7, comprising one or more of the following features orsteps: (a) producing an alarm signal if the number of pulses detectedwithin a size range of 1 to 7 μm is exceeded; (b) converting the data ofnumber of pulses for each particle size into a histogram of the detectedparticle size distribution, displaying the histogram on an outputdisplay device, and repeating the conversion and displaying steps atpredetermined intervals for new air samples; (c) comparing the histogramto known bio-agent particle size distributions, and activating an alarmif the detected distribution matches any known bio-agent particle sizedistribution; (d) blowing air through the sample area continuously tomonitor changing conditions in a surrounding area; (e) reflecting atleast part of the second portion of the light beam onto a seconddetector, connecting the output of the second detector to a powermonitor for detecting decrease in light source output power, andproducing an alarm signal if the light source power falls below apredetermined level; (f) placing a transparent partition slide betweenthe sample area and beam blocking device to prevent dust from enteringoptical components.
 9. A waterborne particle detector system,comprising: an outer housing having an water sample cell area ofcross-section not in excess of about 2 mm; a light source on one side ofthe water sample cell area for directing a focused beam of light throughthe sample air, whereby portions of the beam of light are scattered atvarious angles by particles of various sizes present in the sample area,and an unscattered portion of the beam of light remains unscattered; abeam blocking device on the opposite side of the water sample area forblocking at least the unscattered portion of the beam of light anddirecting at least part of the scattered light along a light path; adetector positioned in the light path after the beam blocking device fordetecting light directed by the beam blocking device onto the detector,and producing output pulses in which each pulse has a heightproportional to particle size; and a pulse height discriminator forobtaining the size distribution of airborne particles detected in theair sample at a given time.
 10. The system as claimed in claim 9,comprising one or more of the following features: (a) an alarm unit forproviding a warning signal if the number of particles within apredetermined size range exceeds a predetermined normal level withinthat size range; and preferably the alarm unit produces an alarm signalif the number of particles detected within a size range of approximately1 to 7 μm exceeds a predetermined level; (b) a processing unit connectedto the output of the pulse height discriminator for processing theparticle size distribution at a given time, based on the height of eachpulse, producing a histogram of the airborne particle size distribution,and displaying the histogram on an output device; (c) a reflectorpositioned in front of the beam blocking device in the path of theunscattered portion of the light beam for reflecting at least part ofthe unscattered portion in a second light path, and a secondphotodetector positioned to detect light reflected from the reflectorand preferably a power monitor connected to the output of the secondphotodetector for detecting decrease in light source output power, andan alarm device connected to the power monitor for producing an alarmsignal if the light source power falls below a predetermined leveland/or possibly a differential amplifier connected to the outputs of thetwo photodetectors for dividing the output of the first photodetector bythe output of the second photodetector, the differential amplifierhaving an output connected to the pulse height discriminator (d) thesample cell includes an inlet and an outlet, and including water tightconnectors on said inlet and outlet with preferably the water tightconnectors being removable. (e) the light source comprises a laser; (f)the light source comprises an LED and preferably also includes opticallens for shaping light from said LED into near collimated light.
 11. Adetector apparatus for detecting waterborne particles in a size range ofapproximately 1 to 20 μm in water, comprising: a light source fordirecting a focused beam of light through a sample of water air in asample cell of cross-section not in excess of about 2 mm, whereby afirst portion of said light beam remains unscattered and a secondportion of said light beam is scattered at various angles by particlesof various sizes present in the water sample, the scattering angle andscattering cross-section being dependent on the particle size; a beamseparating device for separating a predetermined part of the light beamcorresponding to light scattered by particles within a predeterminedsize range from the remainder of the light beam and directing theseparated part of the light beam along a light path; and a detectorpositioned in the light path for detecting said separated part of thelight beam and producing a corresponding output signal includinginformation on the number of particles in the light path within apredetermined size range.
 12. The system as claimed in claim 11,comprising one or more of the following features: (a) a control unitconnected to the detector output for generating an alarm signal if thedetected number of particles within a range of approximately 1 to 20 μmin size exceeds a predetermined value; (b) a pulse height discriminatorconnected to the output of the detector for separating and countingoutput pulses from the detector based on pulse height, a processing unitconnected to the output of the pulse height discriminator for processingthe particle size distribution at a given time, based on the height ofeach pulse, and producing an output comprising a histogram of theairborne particle size distribution, and a display device connected tothe output of the processing unit for displaying the particle sizedistribution histogram; (c) a reflector positioned in front of the beamseparating device in the path of the unscattered portion of the lightbeam for reflecting at least part of the unscattered portion in a secondlight path, and a second photodetector positioned to detect lightreflected from the reflector, and preferably a power monitor connectedto the output of the second photodetector for detecting decrease inlight source output power, and an alarm device connected to the powermonitor for producing an alarm signal if the light source power fallsbelow a predetermined level and/or preferably a differential amplifierconnected to the outputs of the two photodetectors for dividing theoutput of the first photodetector by the output of the secondphotodetector, the output of the differential amplifier having an outputconnected to the pulse height discriminator; (d) a transparent partitionslide positioned between the sample area and the beam separating device;(e) the light source comprises a laser; (f) the light source comprisesan LED; and preferably optical lens for shaping light from said LED intonear collimated light.
 13. A method of detecting waterborne particles,comprising the steps of: directing a light beam through a sample ofenvironmental water in a sample cell of cross-section not in excess ofabout 2 mm such that a first portion of the light beam is scattered byparticles present in the sample and a second portion remainsunscattered; receiving both portions of the light beam which have passedthrough the air sample and directing the light beam portions onto a beamblocking device; blocking at least the second portion of the light beamat the beam blocking device and directing at least part of the firstportion of the light beam onto a first detector; measuring the pulseheight of electrical pulses output from the first detector; counting thenumber of pulses of each pulse height in a predetermined time interval;and converting the pulse heights to particle sizes.
 14. The method asclaimed in claim 11, further comprising one or more of the followingfeatures or steps: (a) an alarm signal if the number of pulses detectedwithin a size range of 1 to 20 μm is exceeded; (b) converting the dataof number of pulses for each particle size into a histogram of thedetected particle size distribution, displaying the histogram on anoutput display device, and repeating the conversion and displaying stepsat predetermined intervals for new air samples; (c) comparing thehistogram to known bio-agent particle size distributions, and activatingan alarm if the detected distribution matches any known bio-agentparticle size distribution; (d) blowing air through the sample areacontinuously to monitor changing conditions in a surrounding area; (e)reflecting at least part of the second portion of the light beam onto asecond detector, connecting the output of the second detector to a powermonitor for detecting decrease in light source output power, andproducing an alarm signal if the light source power falls below apredetermined level.
 15. A detector system for detecting biologicalorganisms or biological agents of predetermined particle size in a fluidcomprising: a housing having a passageway to allow for a fluid to flowthrough the housing; a first light source for sending a light beamthrough the fluid flowing in the passageway; a detector positioned inthe light path of the first light source after said passageway fordetecting and discriminating between particles of a selected size rangein the fluid; a second light source for sending light through said fluidpassing in the passageway for exciting fluorescence in the particles insaid fluid; an elliptical mirror for collecting fluorescence lightsignals generated at one of the foci of the ellipsoid and directing thecollected fluorescence light signals to a photo-detector located at theother focus of the ellipsoid; a detector positioned in the light path ofsaid second light source for detecting fluorescence of said particles;and a control circuit connecting to outputs from said first and seconddetectors for generating an alarm output signal under selectedconditions.
 16. The apparatus of claim 15, comprising one or more of thefollowing features: (a) the first light source and a second light sourcecomprise a single light source; (b) wherein the fluid comprises air; (c)wherein the fluid comprises water; (d) wherein the fluid comprises airand the particles are of size from about 1 to about 7 microns; (e)wherein the fluid comprises water and the particles are of size fromabout 1 to about 20 microns; (f) wherein the second light sourceoperates at a wavelength of about 270 nm to about 410 nm, and preferablythe second light source operates at a wavelength of about 370 nm toabout 410 nm.
 17. A filter unit for use with a particle detection sensorcomprising: a chamber; a filter medium for restricting particles orclumps of particles above predetermined size from said chamber; and anoutlet from said chamber for connection to a particle detection sensorsystem.
 18. A fluorescence/particle detection system comprising: apassageway in which a fluid containing biological organisms orbiological agents can flow; a plurality of housing serially connectedalong said passageway; at least one light source in each of saidplurality of housing for sending light through the fluid for excitingfluorescence of said biological organisms or biological agents; adetector positioned in the light path after said passageway fordetecting the fluorescence and particle size of said biologicalorganisms or biological agents and producing a corresponding outputsignal.
 19. The fluorescence/particle detection system of claim 18,comprising one or more of the following features: (a) wherein each lightsource produces light with a different wavelength; (b) wherein eachlight source is tuned to produce light of an optimal excitationwavelength of one or more metabolites; (c) wherein the wavelength of onelight source is suitable for detecting riboflavin (d) wherein thewavelength of one light source is suitable for detecting NADH; (e) along-wavelength optical pass filter in the path of the light beam beforethe fluorescence sensor to eliminate the excitation laser light; (f)wherein said detector contains wavelength-selective elements to dospectral analysis of the light; (g) wherein said plurality of sensorsmeasure the fluorescence of the same batch of fluid; (h) wherein eachhousing contains two light sources and one light source in each housinghaving a common wavelength to ensure consistent particle sizemeasurements; (i) wherein said fluid is air; (j) wherein said fluid iswater; (k) wherein the wavelength of one light source is about 270 nm toabout 410 nm.
 20. A method of detecting biological organisms orbiological agents, comprising the steps of: directing a plurality oflight beam through a fluid such that a portion of the light excitesfluorescence of said biological organisms or biological agents;detecting the fluorescence and particle size of said biologicalorganisms or biological agents with a detector positioned in the lightpath and producing a corresponding output signal.
 21. Afluorescence/particle detection system comprising: an housing with asample area in which a fluid containing biological organisms orbiological agents can flow; a plurality of light sources for sendinglight beams through the fluid to excite fluorescence of said biologicalorganisms or biological agents; an optical coupler in the path of thelight before the sample area to modulate the plurality of light beams atdifferent frequencies; one or more detectors positioned in the lightpath for detecting the fluorescence and particle size of said biologicalorganisms or biological agents and producing a corresponding outputsignal; an control mechanism to differentiate the plurality of lightbeams based on the modulation frequency of the beam and to producemeasurement of multiple fluorescence signals.
 22. An particle detectorsystem, comprising: an housing having an air sample cell; a light sourceon one side of the air sample cell area for sending a focused beam oflight through the sample air, whereby portions of the beam of light arescattered at various angles by particles of various sizes present in thesample area, and an unscattered portion of the beam of light remainsunscattered; a reflection mechanism placed in the light path fordeflecting into a second light path at least a portion of the lightscattered at a certain range of angles; a first positioned in the secondlight path for detecting a portion of the light and producing acorresponding output signal; a second detector positioned in the lightpath after the reflecting mechanism for detecting a portion of the lightscattered at angles not reflected by said reflection mechanism andproducing a corresponding output signal.
 23. The system as claimed inclaim 22, comprising one or more of the following features: (a) whereinsaid first detector is optimized for measuring particles from 0.1 μm to1.0 μm in size; (b) wherein said second detector is optimized formeasuring particles from 1 μm to 10 μm in size; (c) a mechanism forsplitting the light beam into a plurality of beams placed in the lightpath after the reflection mechanism and before said first detector; athird detector placed in the light path of one of the plurality of beamsfor detecting the fluorescence of particles in the sample area; andpreferably where said mechanism for splitting the light beam is adichroic filter; (d) wherein said second detector contains optics tofocus the reflected portion of the second light beam; (e) wherein saidsecond detector contains optics to remove the unscattered portion of thesecond light beam before detection; (f) wherein said light sourceincludes optical lens for shaping light and/or removing noise from saidlight beam.